The present invention relates to a failure mode control apparatus for an electronic graphic data transmission system such as a facsimile system utilizing a public telephone network.
Fully automatic or unattended facsimile transmission systems utilizing public telephone networks have come into widespread use in many governmental and commercial applications. An original document for transmission is loaded into a scanning unit at the transmitter and a start button is depressed. The transmitter automatically dials the number of the intended receiver. The receiver automatically answers and establishes a telephone circuit. The original document is scanned by the scanning unit which generates electrical signals constituting a digital representation of the document. These signals are transmitted to the receiver and fed to a printer which reproduces a permanent paper copy or facsimile of the document.
Upon completion of scanning of the original document and transmission of the electronic data signals corresponding thereto, the transmitter disconnects itself from the telephone network and resets itself to an initial ready-for-transmission status. The receiver detects the breaking of the telephone circuit and also resets itself to an initial ready-for-transmission status in which the facsimile may be removed for use and fresh copy paper is fed to an operative position in the printer.
However, if a malfunction such as a paper jam or noise interference in the telephone network occurs, a conventional facsimile system is provided with means to automatically break the telephone connection and shut down the transmitter and receiver. In this condition, the receiver is not operable to receive another call and in a system in which each facsimile installation includes both a transmitter and a receiver the transmitting station is further inoperable to receive a call.
In order to overcome this problem the present applicant has proposed in his Japanese patent application No. 50-62509 a failure mode control system which resets both the transmitter and receiver to their initial status at high speed upon detection of disconnection of the telephone circuit by either the transmitter or receiver due to detection of a malfunction during transmission. Although the system provides excellent performance in practical application, it is relatively expensive to implement and is not applicable to low-cost installations.
In facsimile transmission in which the data signals are transmitted in the form of blocks of data bits, errors in the transmission of the blocks account for the great majority of transmission malfunctions which result in automatic disconnection. Apparatus malfunctions and paper jams account for a smaller percentage of disconnections. In applications in which side circuits are employed, the possibility of disconnection due to erroneous operation of switchboards in the public telephone network is quite small.